technical question on center ch. of Dolby Digital

[dondeaida]

Hello, thank you for reading my post.

My question is regarding to center ch. of Dolby Digital. My understanding is that, in Dolby Digital, low frequency signals that are contained in 5 ch. (fl, fr,bl, br, center) are redirected to the LFE ch.

My question is: Is it possible to encode full frequency range (yes, full frequency including low frequencies that would normally get seperated and encoded into LFE ch.) into center ch. ?

Are there some sort of technical provisions that bar encoding full frequency range into center ch. ? My guess is no there is not. Am I right?

I guess above question could be rephrased into: At what stage the seperation of frequency occur? At the time of encoding or at the time of decoding (at speaker amplifier)?

My guess is that seperation of frequency is not required at the time of encoding, that is, I may encode so that each and every 6 ch. have full frequency signal (because non-applicable frequencies for each ch. will be ignored anyways at the time of decoding). Am I right on this?


To sum up, what I really want to know is -->

1.
If it is possible to encode full frequency range into center ch.

2.
And if answer is yes, will the SPDIF jack at the back of the DVD player unit output this full frequency of center ch. as is without filtering the low frequency? (regardless the low frequency of center ch. will be ignored at the later stage by the speaker amplifier or not)
Or will the SPDIF output ciruit in DVD player unit (not the circuit in the speaker amplifier unit) somehow filter out the low frequency of center ch.?

I would very much appreciate your expert answer. Thank you and have a great day.

[guns1inger]

You will find that on many DVDs, the LFE is in fact empty, and the LFE is actually controlled by the cutover level set in the amp.

So yes, you can mix down everything into the centre channel if you wish, and everything in the centre channel will be sent through unfiltered. However, when it reaches the amp, the amp will most likely pull the low frequency signals and re-direct them to the subwoofer if there is one connected. This is an amplifier setting, and nothing you can control through authoring.

[dondeaida]

Thank you Guns1inger. I have one more question.

Can I mix down full frequency range (yes including even tweeter-high range) into the LFE channel and still the full range frequency in this LFE channel will be sent through to the amplifier unfiltered??? (And the filtering will only occur at the amplifier, that is, no filtering at the DVD player's output circuit even for this abnormally full frequencied LFE ch.?)

Please also recommend this newbie grasshopper a couple of easy to use and popular DVD authoring software with excellent compatibility with all DVD player units.

Have a great day Guns1inger.

[guns1inger]

I'm not sure what you are trying to achieve with this. I cannot confirm if you can put all of this into the LFE, although I suspect that it is possible. And the digital connection will simply send through what is there to be sent, however what the amplifier will do with the signal is outside your control, and what the subwoofer will make of it I don't know.

Top of the list to consider would

DVD Workshop Pro (Ulead)
DVD Lab Pro (MediaChance) - I use this one myself
DVD Architect Studio (Or DVD Architect if you buy Vegas as well)
Adobe Encore

These are the most feature rich applications within the cost of mortals. Under this would be

Ulead's consumer products
DVD Lab Studio
Tmpgenc DVD Author

[dondeaida]

Thank you.

[Bokir]

Hai,

I just want to add and clarify a bit.

First you really need to separate Dolby Digital encoding/decoding process and Bass Management process. Because actually it's totally a two separate thing.

Dolby Digital is a (proprietary) compressed digital audio format, that allow you to have five discreet full range plus one limited frequency digital audio track.

In true theater/cinema setup, the audio chain consist of five full range speakers channel (with three main speakers on the front, and an array of surround speaker divided as left and right) plus one LFE channel assigned to one (or more) subwoofers (depending on the size of the auditorium).

In that situation, all the track channel goes directly to it appropriate speakers channel, WITHOUT needing any bass management system.

But in home audio setup, most likely limited space (and budget) restrict this setup. As you might aware real full range speaker is expensive and is huge.
Then come, the satellite and subwoofer speaker solution. A pair (or five) of limited range satellite speakers suplemented with a subwoofer in the setup. Now the issue arise, how to direct all the low frequency from the main track to the subwoofer? Thats when we need bass management.

So in short, dolby digital decoding happen when one AC-3 (dolby digital stream) are decoded back to 5.1 channel.
Then in case of satellite + sub speaker are implemented, this 5.1 channel are then enter the bass management system, where all the low frequency content (from the five track) are filtered (by use of audio crossover) and redirected to the subwoofer along with the LFE channel.

Now to answer your question:

1. If it is possible to encode full frequency range into center ch.

-- Yes indeed. You always need to mix full frequency for the main channel.

2. And if answer is yes, will the SPDIF jack at the back of the DVD player unit output this full frequency of center ch. as is without filtering the low frequency? (regardless the low frequency of center ch. will be ignored at the later stage by the speaker amplifier or not)
Or will the SPDIF output ciruit in DVD player unit (not the circuit in the speaker amplifier unit) somehow filter out the low frequency of center ch.?

-- In the case of playing Dolby Digital encoded material--this yellow RCA S/PDIF output an (Dolby) AC-3 stream. So it's still consist of a single multiplexed compressed digital audio stream. That then need to be decoded by the Dolby Digital decoder.
So, yes its five full range channel, including the center channel you mentioned.

Note: The LFE channel already being pre-filtered (120Hz LPF) by the Dolby Digital encoder earlier in the process.


Okay. Thats about it. If I miss something please let me know.